Microstructure and mechanical properties of free and restrained dried paper: a comprehensive investigation

The influence of strain during drying is known to have a large effect on its mechanical properties like tensile strength, Young’s modulus and hygroexpansion. In this study we investigate free and restrained dried paper and investigate the relation between the paper microstructure and its mechanical properties. The first part of the work investigates the development of the mechanical properties as well as paper internal stresses and strains (elastic-, inelastic- and hygrostrain) at different moisture contents during the drying process. Emphasis is put on the changes of hygrostrains and the paper hygroexpansion coefficient during drying. One main finding was that in constrained drying the drying stresses are considerably below the yield stress and, as a consequence, the deformations are mainly inelastic (creep) and only marginally elastic. In the second part we are analyzing the microstructure of free and restrained dried sheets by X-ray microtomography ($$\mu$$ μ -CT). From the $$\mu$$ μ -CT analysis relevant network parameters such as number of contact points, fiber bond area, free fiber length and fiber curl were extracted. Also a novel method to investigate the interface angle of the fibers in the vicinity of the bond sites was established. The results showed that the major difference from the drying procedure manifests itself in the out-of-plane curl of the fibers. Statistically number of contact points, bond area and in-plane curl were not different whereas in-plane curl and free fiber length were different. The interface angle appears to be slightly affected by the drying procedure but is overall very low.

Boundary Control on Embedded Heaters for Composite Joining

This paper demonstrates the use of boundary control on embedded resistive heaters with the purpose of precision temperature control for curing high strength adhesives when joining composite adherends. This is particularly useful in the presence of heatsinks, where a uniform heating technique will lead to temperature variations in the bondline. The major contribution of this work is to reduce such temperature variations by using boundary control on the embedded heater. This technique is demonstrated experimentally for bonding a single-lap joint, and the temperature variation in the bond area was reduced from 20.3% to 2.7%.

The Impact of Explosion Welding Parameters on Al/Cu Laminated Composites Interface

In this study Al/Cu laminated composite specimens were obtained via explosion welding at various modes. Microstructure, chemical composition and microhardness of Al/Cu bond area were investigated by means of optical and SEM microscopy. Four typical microstructures of Al/Cu bond area were identified at different explosion welding parameters. The types included various amounts of molten zones in the structure. The evolution of the molten zone hardness value identified explosion welding regimes which contributed to maximum amount of intermetallic compound formation during explosion welding.

Analysis of Micro-Crack Inducing Mechanism by Graphite in Bond Area in Laser Repairing Grey Cast Iron

Experimental researches are developed on grey cast iron surface to clarify the micro-crack formation mechanism and influence law of graphite phase in bond area. The results show that unreasonable morphology of flake graphite phase in bond area is an important cause of micro-crack initiation and propagation. Their cusps almost cross toward the molten layer and through the bond area. Then the micro-crack grows along the grain boundary. Additionally, under condition of certain specific energy input, an appropriate increase in laser power and scanning speed can enhance molten mass convection. It can be also helpful for the distribution rationalization of graphite phase and reduce crack sources.

Tensioned Pullout Test Used to Investigate Wire Splitting Propensity in Concrete Railroad Ties

An experimental program was done at Kansas State University to investigate the possibility of splitting caused by different wire indent patterns used in concrete railroad ties. 5.32-mm-diameter pre-stressing wires with chevron, dot, or spiral indent patterns were tested along with a smooth wire. The wires were tested using a tensioned pullout test setup that was developed to simulate the transfer length bond area interaction between the wire and the concrete. The wires were tensioned to 75% of their ultimate capacity before the concrete specimens were cast around the wire. Various diameter concrete specimens were tested to determine the amount of cover needed to prevent splitting. The wire was de-tensioned when the concrete had reached 4,500 psi, during which time wire slip and force were measured on each side of the specimen. The spitting behavior found during this testing was used to determine the probability of a wire to cause potential splitting in a concrete railroad tie. Indent geometry data was also compared with this test data to determine a method for predicting the splitting potential based on indent geometry.

Towards 3D analysis of pulp fibre networks at the fibre and bond levels

By using X-ray synchrotron microtomography imaging, this work aims at proposing a method to get 3D information on paper fibrous microstructures. Such technique is useful to better understand the links between the manufacturing conditions, the resulting microstructural and mechanical properties of the paper fibrous networks, together with the morphology of fibres and fibre-fibre bonds. Its usefulness is illustrated for the 3D analysis of model papers being produced by changing the wet pressing conditions. It is demonstrated that the image analysis allows the changes of parameters describing, for example, the fibre cross section shape and inclination, the bond area surfaces, the distance between bonds to be followed with respect to the processing conditions for a large set of fibres and bonds. The distributions of properties that can be drawn from this experimental analysis will allow mechanical or physical discrete modelling approaches for papers to be enriched.